1. Field of the Invention
The present invention relates to an arylamine compound, a charge transport material, an electrophotographic photoreceptor, an image forming apparatus, and a process cartridge.
2. Description of the Related Art
A photosensitive receptor having a photosensitive layer mainly containing an organic photoconductive compound has been actively studied owing to various advantages thereof, for example, it is relatively easily produced, is inexpensive, and is easy to handle, and is excellent in thermal stability, in comparison to the conventional photoreceptor mainly containing an inorganic photoconductive material (such as, selenium, zinc oxide, cadmium sulfide and silicon) having been used in the art. In particular, a photoreceptor having a function-separated photosensitive layer with an accumulated layers has been put into practical use, in which the charge generation function and the charge transport function are borne by separated functional layers, and a material having the former generation function is contained in the charge generation layer, whereas a material having the later charge transport function is contained in the charge transport layer.
There is such a possibility in this system that a substance having a large charge generation efficiency is used as the charge generation material, and a substance having a large charge transport efficiency is used in combination thereto as the charge transport material, whereby a electrophotographic photoreceptor having high sensitivity can be obtained. Low molecular weight compounds have been mainly used as the charge transport material, which are generally used after dissolving in an organic solvent along with a suitable binder resin, followed by coating. The system is preferred since the property of the coated layer and the photosensitive characteristics can be controlled to a certain extent by selecting the kind and the compositional ratio of the binder resin. However, in order to form a uniform organic thin film that does not suffer deposition of crystals or formation of pinholes, it is necessary to select a charge transport material having high compatibility to the binder resin.
Furthermore, it is important that charge injection from the charge generation material to the charge transport material, i.e., charge injection from the charge generation layer to the charge transport layer, is effectively carried out though the charge generation material and the charge transport material have good characteristics. The charge injection cannot be determined unconditionally among the substances since it depends on the characteristics of the interface between the charge generation material (or the charge generation layer) to the charge transport material (or the charge transport layer). As having been described, the charge transport material is demanded to satisfy various conditions, and thus charge transport materials having various characteristics have been developed.
Among them, a tetraarylbenzidine compound has been earnestly studied owing to the high charge mobility (as described, for example, in U.S. Pat. No. 4,047,948, U.S. Pat. No. 4,299,897, JP-A-61-132955, JP-A-62-267749 and JP-A-3-138654). Among the tetraarylbenzidine compounds, one having a styryl group as a substituent has been known (as described, for example, in JP-A-4-290851, JP-A-6-11854 and JP-A-7-36203).